Osteomyelitis is infection in the bones. Often, the original site of infection is elsewhere in the body, and spreads to the bone by the blood. The bone may be predisposed to infection due to a recent minor trauma that results in a blood clot or hemostasis. In children, the long bones are usually affected. In adults, the vertebrae, head, and the pelvis are most commonly affected. Bacteria or fungi are the usual organisms, but any microbe may be responsible for the infection. Pus is produced within the bone, which may result in a bone abscess. The abscess then deprives the bone of blood supply. Chronic osteomyelitis results when the causative microbes become resistant to antimicrobial agents. This may occur due to development of cellular mechanisms to circumvent the antimicrobial agents, formation of biofilms which allow quiescent organisms to remain untouched by antimicrobial agents, death of bone tissue as a result of the lost blood supply, and other mechanisms. Chronic infection can persist for years with intermittent exacerbations. Risk factors for chronic infection are recent trauma, diabetes, hemodialysis patients, IV drug abuse, and infection with organisms that are more adept at forming biofilms or developing antimicrobial resistance. Tuberculous osteomyelitis is caused by tubercle bacilli that enter the bloodstream and settle in a bone. The disease progresses slowly and is chronic. Any bone may be infected but those most commonly involved are the vertebrae. Spinal tuberculosis, or “Pott's disease” causes bone destruction and spinal deformities. Other bones that may be affected are the longer bones of the hands or feet. The total incidence of osteomyelitis is 2 out of 10,000 people.
Symptoms of osteomyelitis primarily include pain in the bone, bone tenderness, local swelling and warmth (facial swelling), fever, nausea, general discomfort, uneasiness, or ill feeling (malaise), and drainage of pus through the skin in chronic infection. Additional symptoms include sweating, excessive chills, back pain, and low-grade swelling of the ankle, feet, or the leg. Osteomyelitis is diagnosed through physical examination showing bone tenderness, swelling and redness, elevated white blood cell count, elevated ESR, blood cultures that identify the causative organism, needle aspiration of vertebral space for culture, bone lesion biopsy and culture, bone scans, and drainage of a skin lesion with a sinus tract (the lesion “tunnels” under the tissues) for culture.
The outcome of treatment for acute osteomyelitis is usually good, but when treatment of acute osteomyelitis fails the outcome of treatment for chronic osteomyelitis is worse, even with surgery. Chronic infection may result in bone destruction, in stiffening of joints if the infection spreads to the joints, and, in extreme cases occurring before the end of the growth period, in the shortening of a limb if the growth center is destroyed. Resistant chronic osteomyelitis may result in amputation and can threaten life through seeding of the microorganisms to cardiac valves, the lungs, and the brain.
Treatment for osteomyelitis focuses on eliminating the infection and preventing the development of chronic infection. High-dose intravenous antibiotics are given initially. The type of antibiotics and the route of administration may later be changed depending on culture results. Typical lengths of treatment for acute osteomyelitis vary from 6 weeks to 6 months depending on the organism and the anatomy of the infection site. In chronic infection, surgical removal of dead bone tissue is indicated. The open space left by the removed bone tissue may be filled with bone graft or by packing material to promote the growth of new bone tissue. Antibiotic therapy is continued for at least 3 weeks after surgery. Infection of an orthopedic prosthesis requires surgical removal with debridement of the infected tissue surrounding the area. A new prosthesis may be implanted in the same operation, or delayed until the infection has resolved, depending on its severity. Estimates of the percentage of acute osteomyelitis cases that become chronic osteomyelitis cases vary from about 10% to about 30%. Once the osteomyelitis has become chronic, biofilms or abscesses usually have developed, protecting the microbes from treatment with antibiotic drugs.
The currently available antibiotic treatments are expensive, inconvenient, frequently ineffective, and subject to many complications. Thus, there is a need for additional therapies for osteomyelitis.